Chapter 3 Response and Coordination Notes

Chapter 3 : Response and Coordination Notes and exercises form 5 Biology – Tn Hj Mohd Hafiz (www.cikguhafiz.com)
Chapter 3: Response and Coordination ©MHMS www.cikguhafiz.com 1
External
environment
Sound
Smell
Taste
TemperaturePressure
Light
Touch
Internal
environment
Blood
pressure
Body
temperature
Sugar level in
blood
pH level in
blood
In Human
Help to survive
Ensure the metabolic
activities are carried out
at optimal environment
In Animal
Protect themselves from
changes in external
environment
Sensitive to presence of
female animal by the male
for reproduction
Help to move to find food
from one place to another
In Plant
Enable plant to move
toward sunlight
Enables plants to absorb
water and mineral salt.
FORM 5 BIOLOGY NOTES
CHAPTER 3 : RESPONSE AND COORDINATION
By: Tn. Hj. Mohd Hafiz Bin Mohd Salleh
3.1. Response and Coordination
Definition:
 Stimulus - A change in external or internal environment in the body which can be detected by the body’s
system. (plural : stimuli)
 Response - An action of the body, either consciously or unconsciously towards a certain stimulus.
 Receptor - A group of cells in the body specialised to detect the changes in the external or internal
environment in the body.
 Coordination - The control of different parts of organs and systems that makes them working together
effectively and efficiently.
Changes in External and Internal Environment Faced by an Organism:
Necessity for Living Organisms to Respond To Stimuli:

Pathway in Detecting And Responding To Changes
Pathway Information Due To External Stimuli
Pathway Information Due To Internal Stimuli

3.2. Role of Human Nervous system
Human being must MONITOR and MAINTAIN constant internal environment as well as monitor and responds to
external environment
Definition:
 NERVOUS SYSTEM is the system that monitors, maintain and responds to environment. (External @ Internal)
Role of nervous system:
1. The nervous system collects information about the changes in internal and external environment.
2. The nervous system transmits information about the changes in internal and external environment via the
neurons to the processing centre.
3. The nervous system process, integrates and interprets the information received.
4. The nervous system coordinates the body activities and brings about appropriate response.
Organisation of nervous system

PERIPHERAL NERVOUS SYSTEM
 Cranial nerves - Send nerve impulse to and from the brain.
- Smell, vision, hearing, movement of eyeball and movement of head and shoulder.
 Spinal nerves - Send nerves to and from the spinal cord.
- Contain sensory neurons and motor neurons.
Structure and Function of Brain
1. The brain consists of three main parts :
a) Cerebrum
b) Cerebellum
c) Brain Stem (Medula Oblongota)
1. Below the centre of the cerebrum is the thalamus,
hypothalamus and pituitary gland.
2. The brain is made up of nerve cells called neurones.
3. The outer part of the brain consists of the grey matter
[cerebral cortex] ( which contains the cell body of the
neurone ) and the inner part consists of the white
matter ( which contains the fibres of the neurone ).
Cerebrum
1. The cerebrum is the largest and most complex part of the
brain.
2. It is divided into two halves called the cerebral hemispheres.
3. The left hemisphere controls the movements on the right
side of the body.
4. The right hemisphere controls the movements on the left
side of the body.
5. The cerebral hemisphere is divided into regions containing
specialised groups of nerve cells responsible for sensory,
motor and association functions.
6. The interrelationship between these three areas enables the
cerebrum to control and coordinate all voluntary activities of the body, including highly-developed
functions such as memory, reasoning, learning and speech.
7. Cerebrum control: Learning, Memorising , Speech, Mathematical skill, Imagination, reasoning, Planning,
Touch, Taste, Temperature, Movement, Sight, Hearing, Memory retrieval .
Hypothalamus
1. Located on the ventral region of the cerebrum.
2. Pituitary gland is located at the end of the hypothalamus.
3. Hypothalamus has the richest blood supply in the brain.
4. It acts as a major coordinating centre for regulating: sleep, hunger,
thirst, body temperature, water balance and blood pressure.
5. For example, it detects changes in blood temperature and osmotic
pressure. If there are any changes, it will initiate nerve impulses to

the effectors to produce homeostatic responses required for regulation of the body temperature and the
osmotic blood pressure.
6. Thus, hypothalamus helps to regulate body temperature and osmotic blood pressure through the pituitary
gland.
7. Hypothalamus also control centre of the endocrine system.
Thalamus
1. Located on the region of cerebrum , above the hypothalamus
2. The thalamus is responsible for sorting the incoming and outgoing
information in the cerebral cortex.
3. It also integrates the information from the sensory receptors to the
cerebrum by enhancing certain signals and blocking others.
4. Thalamus is also the integration centre for sensory impulses such as
sight and hearing to the various sensory areas of the cerebrum.
Pituitary gland
1. The pituitary gland secretes hormones that influence other glands and body functions.
2. The hypothalamus controls the release of several hormones from the pituitary gland and thereby serves as
an important link between the nervous and endocrine systems.
Cerebellum
1. The cerebellum is located below the cerebrum near the top of
the spinal cord. It has a folded surface. The cerebellum has two
hemispheres.
2. Functions of cerebellum :
a) Coordinates the contraction of muscles
b) Controls the posture and balance of the body.
Medula oblangota
1. Located in front of the cerebellum.
2. Medulla oblongata links the brain to the spinal cord.
3. Functions of medulla oblongata :
a) Controls and regulates involuntary actions such as
the rate of heartbeat, peristalsis, blood pressure,
breathing and the variation in the size of blood
vessels during vasodilatation or vasoconstriction.
b) Centre for certain reflex actions such as vomiting,
coughing, sneezing and swallowing.

Structure and Function of Spinal Cord
1. Spinal cord linked between the brain and the peripheral nervous
system.
2. It consists of grey matter in middle and white matter.
3. Spinal nerves arise from the spinal cord and spinal nerve has a
dorsal root which contains the afferent neuron and ventral root
which contains the efferent neuron.
4. Spinal cord control reflex action.
5. The spinal nerves emerge from the spinal cord through two
short branches or roots.
a. The dorsal root contains the axons of the afferent
neurones which conduct nerve impulses from the
sensory receptors to the spinal cord.
b. The cell bodies of the afferent neurones are
clustered in the dorsal root ganglion.
c. The ventral root contains the axons of the efferent
neurones which conduct nerve impulses away from
the spinal cord to the effectors.
d. The dorsal and ventral roots join to form a spinal
nerve.
Structure of a neuron
1. The cells that carry information through the nervous system are called neurons.
2. The message that a neuron carries is in the form of electrical signal called a nerve impulse.
3. A neuron contain:
a. A large cell body contain nucleus.
b. Dendrites are the threadlike extension from the cell body.
c. Axon is the long fibre from the cell body. It carry impulse away from the cell body.
d. Axon terminals are the branches of the axon.
e. Synaptic knobs is the swelling end of the axon terminals.
f. Axon is surrounded by an insulating membrane known as myelin sheath.
g. Myelin sheath has many gaps called node of Ranvier. It allows an impulse moves by jumping from one
node to the next and increase the speed.

Type of neurons
i. Sensory neurones ( afferent neurones )
 Has a long dendrites and short axon.
 The cell body is located in the ganglion of the dorsal root of the spinal cord.
 Transmit nerve impulses from receptors or sensory organs to the central nervous system (CNS).
ii. Interneurones
 Found within the brain and spinal cord.
 Has a short dendrites and short axon.
 The cell body is located in the grey matter of
the CNS.
 Connects one neurone to another neurone
and frequently connects a sensory neurone
to a motor neurone.
iii. Motor neurones ( efferent neurones )
 Transmit nerve impulses from the central nervous system to the motor organs or effectors, usually
muscles or glands to produce response.
 Have a short dendrites and long axons.
 The cell body is located in the grey matter of the spinal cord.
Axons of many neurons are surrounded by Schwann cells. A large number of Schwann cells cover the axon
several times, forming a myelin sheath .These myelin sheaths contain lecithin, a type of phospholipids, which is an
electrical insulator. Its Enable fast transmission of impulses in the neuron. Nodes of Ranvier are region of the
axon not covered by myelin sheaths

Transmission of Information along the Neuron
Structure and function of synapse
1. Neurons are not directly connected. There
is a gap between two neurons. This narrow
gap is called synapse.
2. Synapse is formed between the axon
terminals of a neuron with the dendrite of
another neuron.
3. The terminal dendrites of axons contain
synaptic knobs.
4. These knobs contain numerous
mitochondria and synaptic vesicles which
filled with neurotransmitters.
5. Examples of neurotransmitters are
acetylcholine , noradrenaline , serotonin
and dopamine

Transmission of chemical signals across the synapse

Types of Coordinated response
There are two types of coordinated response:
1. Voluntary action
2. Involuntary action
Voluntary action
1. Voluntary action is a conscious action and is controlled by the cerebrum of the brain.
2. Voluntary action occurs according to the will of an individual.
1. It involves the process of integration and interpretation of information to produce a response according to
the will.
2. Voluntary action involves the sensory organs, the cerebrum and the effectors (muscles or glands).
Involuntary action
1. Involuntary action is an automatic action that is not controlled by the will of an individual.
2. Involuntary action is controlled by the medulla oblongata.
3. It occurs in the body without any conscious control.
4. Examples of involuntary actions in the body are peristalsis, heartbeat and breathing.
5. The stimuli received by the receptors are internal stimuli.
6. The nerve impulses generated are sent to the medulla oblongata to be integrated and interpreted.
7. The effectors which produce the response are smooth muscles, cardiac muscles and glands.
The differences between voluntary action and involuntary action.
Aspect compared Voluntary action Involuntary action
Type of action Occurs according to the will of an
individual.
Does not occur according to the will of an
individual. It is an automatic action.
Integrating centre Cerebrum Medulla oblongata
Stimulus Involves external stimuli Involves internal stimuli
Receptor Sensory organ Specialised internal receptors
Transmission of
impulse
Impulses transmit from the brain to the
skeletal muscles
Impulses transmit from medulla
oblongata to smooth muscles, cardiac
muscles and glands.
Effector and
response
The effector (skeletal muscles)
produces a voluntary action. For
example, kicking a ball.
The effectors (smooth muscles of
internal organs, cardiac muscles of the
heart and glands) produce involuntary
responses such as heartbeat and
peristalsis.

Reflex Action
1. Reflex action is an involuntary action that occurs automatically and spontaneously without conscious control
towards a stimulus.
2. Reflex action is controlled by the spinal cord and does not involve the cerebrum.
3. It acts as a protection against injuries and dangerous situations, as well as an adaptation to any changes in the
environment.
4. Examples of reflex action are :
a) Knee jerk
b) Withdrawal of the hand from a hot object
c) Blinking of the eyes
d) Changes in the size of pupil in the eye
e) Balancing the body to prevent from slipping
Reflex Arc
1. Reflex arc is the pathway that a nerve impulse travels from the receptor to the effectors in a reflex action.
2. A reflex arc consists of the receptor, afferent neuron, and interneuron in the spinal cord, efferent neuron and
effectors.
3. The process of a reflex arc :
1. The receptor detects a stimulus and triggers the afferent neuron to send out nerve impulses
2. The nerve impulses are carried by the afferent neuron to the spinal cord
3. From the spinal cord, the nerve impulses travel along the efferent neuron to the effectors without
passing through the brain.
4. The effector receives the information and produces an automatic response towards the stimulus.
Knee jerk

Withdrawal of the hand from a sharp object

Involuntary action which involves smooth muscles, cardiac muscles or gland
1. The autonomic nervous system
 Control involuntary action involving the glands, the cardiac muscles of the heart and the smooth
muscles of the internal organs such as the intestines.
 Connects the medulla oblongata and hypothalamus with the internal organs and regulates the internal
body processes that require no conscious effort.
 Since the information for involuntary actions does not involve the cerebral cortex of the cerebrum, no
perception is generated. Therefore, we are not aware of the responses.
2. This means the autonomic nervous system permits vital functions such as the heartbeats and blood circulation
to continue even during states of unconsciousness such as sleeping or fainting when voluntary actions have
ceased.
3. The autonomic nervous system can be divided into
 The sympathetic division
1. Prepares the body for stressful situations or an emergency, in which the responses are
associated with ‘fight or flight’.
2. Increases the pulse rate, blood pressure, and breathing rate.
3. Slows down the digestive system so that more blood is available to carry oxygen to the vital
organs such as the brain, heart and muscles.
 The parasympathetic division
1. Prepares the body during ordinary situations or brings on the responses associated with a
relaxed state.
2. Decreases the pulse rate, blood pressure, and breathing rate.
3. Stimulates the digestive system to continue breaking down food.
Diseases Related to the Nervous System
1. Alzheimer’s disease
 A neurodegenerative disease characterised by progressive cognitive deterioration, such as loss of
intellectual ability and memory.
 The diseases are associated with the shrinkage of the brain tissue and the changes in the neurotransmitter
system such as lack of acetylcholine in the brain.
2. Parkinson’s disease
 A disease of the nervous system that affects the part of the brain which controls the actions of the muscles.
 The muscles become weak and stiff, causing tremors and jerkiness in movement.
 This is due to the reduced level of a neurotransmitter called dopamine in the brain. In some cases, it is
caused by the hardening of cerebral arteries.
 This disease cannot be inherited.
 Symptoms of Parkinson’s disease are :
o Slow movement due to stiffness and tremor
o Jerkiness
o Weak muscles
o Muscles stiffness and cramps
o Impaired balance and coordination.

3.3. Role of Hormones in Humans
1. Endocrine system is a system controls the body’s activities by releasing chemicals called hormones.
2. Hormones are specific chemical messenger molecules in the bloodstream that can regulate the activities of organs
and tissues. It synthesized by a group of specialized endocrine glands.
The differences between the endocrine system and the nervous system
The nervous system The endocrine system
Controls voluntary and involuntary actions Controls involuntary actions
Conveys electrical signals (nerve impulses) Conveys chemical signals (hormones)
Messages are conducted via neuron Messages are conveyed via the bloodstream
Messages are conveyed rapidly Messages are conveyed slowly
Messages are carried between specific locations Messages are carried from the source to various
destinations
The responses or effects are temporary The responses or effects are long-lasting
Role of Endocrine system
1. Endocrine system is made up of ductless glands that produce and secrete hormones.
2. The endocrine system regulates various physiological processes which are not directly regulated by the nervous
system such as :
a. Growth
b. Reproduction
c. Metabolism
d. Menstrual cycle
e. Development of secondary sexual characteristics
3. Endocrine system and the nervous system work together to regulate the balance of the internal environment
through the process called homeostasis.
4. Endocrine system complements the nervous system in carrying out various body process.

Endocrine Glands and Hormones
Hormones can be divided into three main categories:
i. Reproduction
i. Follicle stimulating hormone ( FSH )
ii. Luteinising hormone ( LH )
iii. Estrogen
iv. Progesterone
v. Androgen
ii. Growth
i. Growth hormone
ii. Thyroid-stimulating hormone ( TSH )
iii. Thyroxine
iii. Homeostasis
i. Insulin
ii. Glucagon
iii. Antidiuretic hormone
iv. Adrenaline
Hypothalamus
Hypothalamic
releasing hormones
Stimulate the secretion of the anterior
pituitary hormones
Hypothalamic
inhibiting hormones
Suppress the secretion of the anterior
pituitary hormones
Anterior pituitary gland (master gland)
Growth Hormone
(GH)
Stimulates growth, protein synthesis and
fat metabolism
Prolactin (PRL) Stimulates milk synthesis and secretion
from the mammary glands
Thyroid-stimulating
hormone ( TSH )
Stimulates the thyroid gland to release
thyroxine
Adrenocorticotrophic
hormone ( ACTH )
Stimulates the adrenal cortex to release
hormones
Follicle-stimulating
hormone ( FSH )
Stimulates the development of the
follicles in the ovaries in females
Luteinising hormone
( LH )
Stimulates ovulation , development of
corpus luteum and secretion of oestrogen
and progesterone in females
Stimulates the secretion of testosterone
in males.
Posterior pituitary gland
Antidiuretic hormone
(ADH)
Stimulates water reabsorption by the
renal tubules in the kidneys
Oxytocin Stimulates the contractions of the uterine
muscles during childbirth; and stimulates
lactation (the release of milk from the
mammary glands in females)

Thyroid gland
Thyroxine Increases the metabolic rates of most body cells
Increases body temperature
Regulates growth and development
Thymus gland
Thymosin Stimulates the formation of T-cells which help defend the body from pathogens.
Adrenal cortex
Aldosterone Increases the reabsorption of mineral salts in the kidneys
Adrenaline and
noradrenaline
Increases the levels of sugar and fatty acids in the blood
Increases heart activity, and the rate and depth of breathing
Increases the metabolic rate and constrict some blood vessels
Pancreas gland
Insulin Decreases blood glucose levels and promotes the conversion of glucose to glycogen
Glucagon Increases blood glucose levels and promotes the conversion of glycogen to glucose
Ovary
Oestrogen Stimulates the development of the female secondary sexual characteristics and maturation
of the ova.
Promotes the repair of the uterine lining
Progesterone Stimulates the development of the uterine lining and the formation f the placenta
Inhibits ovulation
Testis
Androgen
(testosterone)
Stimulates the development of male secondary sexual characteristics and spermatogenesis
Secretion of hormones regulated by another hormone
1. The release of thyroxine is regulated by the thyroid-stimulating hormone ( TSH ).
2. A high level of thyroxine inhibits the release of TSH and stops the release of additional thyroxine.
3. A low level of thyroxine stimulates the secretion of TSH which then stimulates the thyroid gland to secrete
thyroxine.

Secretion of hormones regulated by levels of certain substances
1. Certain hormones are regulated by the level of specific substances in the blood.
2. After a meal, the blood glucose level rises and will promote the release of insulin into the blood stream by the
pancreas.
3. Insulin will cause cells to take up glucose and also cause liver and skeletal muscle cells to form the glycogen.
4. If the glucose level in the blood falls, further insulin production is inhbited.
5. Glucagons are released to break down the glycogen into glucose. Then the glucose is released into the blood to
maintain glucose level.
6. Glucagon production is inhibited when the level of glucose rises.
7. Insulin is an example of hormone and glucose is an example of specific substances.
Secretion of hormones regulated by nervous system
1. When faced with stimuli that are threatening, dangerous or exciting, our body goes through a series of changes
that prepares us to either fight or to flee.
2. The fight-or-flight strategy is a safety measure that prepares the body
to respond to the situation.
3. The fight or flight response involves a coordinated effort of both the nervous and the endocrine systems.
A. The nervous system in the fight or flight response
1. When a threatening stimulus is received, the hypothalamus activates the nervous system (the sympathetic
nervous system) to send impulses to the adrenal medulla to release adrenaline (and noradrenaline) into the
bloodstream.
2. Adrenaline is called the "fight or flight" hormone or the "stress hormone" because it prepares the body for
action.
3. Adrenaline causes:
i. more glycogen to be converted into glucose in the liver
ii. increased metabolic rate
iii. deeper and rapid breathing
iv. a faster heartbeat and a raised blood pressure
v. blood to be diverted from the surface areas of the body and the gut to the muscles
B. The endocrine system in the fight or flight response
1. At the same time, the hypothalamus stimulates the anterior pituitary gland to secrete the adrenocorticotrophic
hormone (ACTH) to activate the adrenal-cortical system.

2. ACTH moves through the bloodstream to the adrenal cortex, where it activates the secretion of corticoid
hormones (approximately 30 different hormones) which will prepare the body to deal with the stress.( raises
blood glucose level by stimulating the conversion of lipids and protein to glucose )
3. The corticoid hormones are slow-acting and have lasting effects.
 In fight and flight situation, The heart contracts more vigorously to pump a larger amount of oxygen and
glucoseto the brain and skeletal muscles.
o The brain needs to be highly alert to mobilise the various parts of the body into immediate action.
o The skeletal muscles become more energised and enable a person to fight off an attacker or flee
immediately from danger.
 When a person is in a stressful situation, the nervous and endocrine system both work together to bring about
immediate responses to cope with the imminent threat.
 Once these mechanisms successfully counteract the danger, the bodily changes that occurred return to normal.
Hormonal imbalances and related diseases
Endocrine gland Hormone Function Effects of hormonal imbalance
Thyroid Thyroxine
• contains
iodine
• important in
growth
 Speeds up cell
 metabolic rate
 Stimulates normal
physical growth and
mental development
 Thyroxine deficiency causes :
a) Cretinism in children (severe mental
retardation )
b) myxedema in adults (sluggishness of
metabolism, swelling of subcutaneous
tissue, disrupted mental and sexual
activities)

 Excessive thyroxine causes:
a) a high metabolic rate
b) an increased rate of heartbeat
c) hyperactivity and
d) goitre in the neck and the eyeballs
protrude.
Adrenal cortex
(produces
corticoid
hormones)
Cortisol Raises blood glucose level
by stimulating the
conversion of lipids and
protein to glucose.
Are produced in response
to stress.
Cortisol deficiency causes Addison disease
 weight loss,
 weak muscles,
 fatigue,
 low blood pressure
 darkening of the skin
Excessive cortisol causes Cushing's Syndrome
 gains weight,
 weak muscles,
 fatigue,
 poor skin healing
 Osteoporosis
Adrenal cortex
(produces
corticoid
hormones)
Aldosterone Regulate blood osmotic
pressure by reabsorbing
Na+ and excreting K+ in the
kidneys to retain water.
Aldosterone deficiency decreases Na+ and
increases K+ ,more water is excreted and
blood pressure drops
Excessive aldosterone increases Na+, decreases
K+ , body retains excess water and blood
pressure increases
Adrenal medulla Adrenaline Prepares the body for
stressful situations by:
 raising respiration and
heartbeat rates
 increasing blood flow
to muscles and brain
 contracting epidermal
arteries and diverting
blood to major muscle
groups (face turns
pale)
 Stimulates the
conversion of glycogen
to glucose.
Excessive adrenaline:
 raises blood pressure
 raises the blood glucose level
 causes glucose to be present in the urine
Posterior
pituitary gland
Antidiuretic
hormone (ADH)
Stimulates the kidney to
reabsorb water and
produce less urine.
 An inability of the posterior pituitary to
secrete ADH can result in a disorder known
as diabetes insipidus.
 As a result , the person excretes a large
amount of urine.
 People with diabetes insipidus are thirsty
all the time. They often want to drink
liquids frequently.
 Because so much water is lost in the urine,
the person may die of dehydration if
deprived of water for even a day.

Pancreas Insulin
(is secreted by
the -cells)
Lowers blood glucose level
by stimulating
 glucose storage as
glycogen (in muscle and
liver), fats (in adipose
tissue) and protein
 oxidation of glucose in
cell respiration
 Insulin deficiency causes:
a) elevated blood glucose levels
b) glucose to be excreted in the urine
(diabetes mellitus)
c) body becomes thin and weak
 Excessive insulin causes
a) low blood glucose levels weakness,
light-headedness, heart beat becomes
rapid and irregular
Glucagon
(is secreted by
the -cells)
Raises blood glucose level
by stimulating the
conversion of glycogen to
glucose
 Glucagon deficiency makes a person weak
and lacking energy
 Excessive glucagon causes a person to be
over active
3.4. Homeostasis in Humans
(Homeostasis : the regulation of the physical and chemical factors in the internal environment to maintain a
constant internal environment)
Necessity to maintain internal environment at optimal conditions
a) Constant internal condition for the survival of organisms.
b) Monitoring changes in the external and internal environments and adjusting the change through a negative
feedback mechanism.
Changes in Blood Osmotic Pressure to Urine Output
1. Water content of blood determines the blood osmotic pressure.
2. Osmotic pressure of blood increase when water loses from body through urinating or sweating.
a. So blood plasma becomes hypertonic to the blood cell.
b. The content of water in the body need to regulate through homeostasis to maintain the optimal level.
c. More water is reabsorbed into the blood by the kidneys.
d. Amount of urine eliminated will decrease.
3. When osmotic pressure in blood is low, it is because high water content in the blood.
a. Less water is reabsorbed into the bloodstream.
b. Excess water from the kidneys is eliminated as urine. This will increase the volume of urine.
Structure of Kidney
1. The kidneys filter blood and form urine which exits the body
through the
i. ureters,
ii. urinary bladder and
iii. urethra.
2. Urine is a fluid which consists of
i. water,
ii. urea and
iii. other dissolved wastes, and
iv. some excess nutrients.

3. The human kidney has two distinct regions
i. an outer light-red region called the renal cortex
ii. an inner dark-red region called the renal medulla
4. The renal artery supplies oxygenated blood and nutrients
to the kidney while the renal vein carries away filtered
blood to the body.
5. Each human kidney consists of about one million
nephrons.
NEPHRON
1. The functional unit of a kidney is the nephron.
2. Each human kidney consists of about one million
nephrons.
3. A nephron consists of three major parts:
a) the glomerulus and its associated blood vessels
b) the Bowman's capsule
c) a long, narrow tube called the renal tubule
4. The renal tubule is made up of the
5. proximal convoluted tubule
6. loop of Henle
7. Distal convoluted tubule
8. The distal convoluted tubules of several nephrons join to
a common collecting duct.
9. The Bowman's capsule and both convoluted tubules lie
within the renal cortex, whereas the loop of Henle
extends into the renal medulla.
10. Within the kidney, each nephron is supplied with blood by
an afferent arteriole which is a branch of the renal artery.
11. Each afferent arteriole divides further into a tangled
capillary network called the glomerulus.
12. The capillaries of the glomerulus reunite to form an efferent arteriole.
13. Each efferent arteriole divides to form a network of blood capillaries surrounding the kidney tubules.
14. These capillaries are called peritubular capillaries or the capillary network which eventually join together into
the renal vein.
The structure of Bowman’s capsule
1. The Bowman's capsule is made up of two layers of cells that
surround the glomerulus.
2. The space between the two layers of cells is called the capsular
space.
3. The cells that make up the inner wall of the Bowman's capsule
are called podocytes.
4. The podocytes adhere closely to the endothelial cells of the
glomerulus.

Formation of Urine
1. The formation of urine involves three main processes :
a) Ultrafiltration
b) Reabsorption
c) Secretion
Ultrafiltration process (Bowman’s capsule and glomerulus)
1. Blood enters the glomerulus through the afferent arteriole and
leaves through the efferent arteriole.
2. The blood pressure in the afferent arteriole is high because it is
derived from the renal artery which branches from the aorta. The
diameter of the efferent arteriole is also smaller than the afferent
arteriole.
 As a result, there is a high resistance in the blood flow.
This produces a high hydrostatic blood pressure in the
glomerulus.
3. The high hydrostatic pressure in the blood of the glomerulus causes most of the constituents of the plasma to
be filtered out of the glomerulus (through the thin capillary walls with pores) into the cavity of the Bowman's
capsule.
4. The process where all the constituents of blood plasma are filtered under high hydrostatic pressure into the
Bowman's capsule is known as ultrafiltration.
5. The fluid filtered into the Bowman's capsule is called glomerular filtrate.
6. The filtrate in the Bowman's capsule consists of all the constituents of the blood plasma in the afferent
arteriole except (which are too large to pass through the capillary walls of the glomerulus)
 erythrocytes,
 leucocytes,
 platelets and
 plasma proteins
7. The glomerular filtrate consists of mainly dissolved small molecules such as
 inorganic ions, especially sodium ions,
 glucose,
 amino acids and
 urea.
Reabsorption process
1. From the Bowman's capsule, the glomerular filtrate flows into the uriniferous tubule.
2. The reabsorption process occurs along the whole uriniferous tubule. Essential solutes and water in the filtrate
are reabsorbed into the blood capillaries that surround the tubule.
3. At the proximal convoluted tubule :
i. About 75% - 80% of water is reabsorbed back into the blood capillaries by osmosis. This occurs because
the glomerular filtrate is hypotonic to the blood plasma.
ii. All glucose, amino acids and some mineral ions like sodium ions ( Na+
) and chloride ions ( Cl-
) in the
tubule are reabsorbed into the bloodstream by active transport.

4. At the loop of Henle :
i. About 15% of water is reabsorbed through
osmosis on the descending limb which is
permeable to water but not to other solutes.
ii. Sodium ions and chloride ions are actively
transported out of the filtrate on the
ascending limb which is less permeable to
water.
5. At the distal convoluted tubule and the collecting
duct:
i. The amount of water and inorganic ions (salts)
that will be reabsorbed from the filtrate
depends on the body's needs and is controlled
by the endocrine system.
ii. The rate of reabsorption of water and salts is affected by the quantity of water and salts consumed. It is
controlled by hormones as the walls of the distal convoluted tubule and the collecting duct are more
permeable to water if antidiuretic hormone (ADH) is present and more permeable to salts if
aldosterone hormone is present.
iii. Urea is not reabsorbed throughout the nephron and is excreted in the urine.
6. The remaining filtrate in the tubule which is channelled into the pelvis of the kidney is called urine.
i. If plenty of water from the filtrate is reabsorbed in the distal convoluted tubule and the collecting duct,
then the amount of urine produced is little and concentrated (hypertonic urine).
ii. However, if less water is reabsorbed from the filtrate, a larger amount of diluted urine is produced
(hypotonic urine).
7. Urine consists of
i. 96% water,
ii. 2.5% nitrogenous waste products such as urea, uric acid and creatinine,
iii. 1.5% inorganic ions and
iv. traces of bile pigments.
8. Urine is carried by the ureter from the kidney to the urinary bladder to be stored temporarily and excreted
through the urethra

Secretion
1. Secretion is the process where unwanted substances like urea, uric acid, ammonia, drugs, alcohol, excess salts
and water in the blood are actively transported from the capillaries surrounding the nephron into the kidney
tubule (especially at the distal convoluted tubule).
2. This process helps to remove the toxic and unwanted substances from the bloodstream.
3. Secretion process also helps to regulate the pH level of the blood. For example, when the blood is too acidic,
the hydrogen ions, H+
, are secreted into the filtrate whereas if the blood is too alkaline, the hydrogen
carbonate ions, HCO-
are secreted into the filtrate.
4. Secretion plays an important role in adjusting the urine composition as it passes through the kidney tubule.
Osmoregulation
1. Osmoregulation is the process of regulating the blood osmotic pressure by regulating the water content and
the concentration of salts in the body.
2. Osmoregulation is an example of homeostasis which is brought about by the negative feedback system.
3. The negative feedback system is a corrective mechanism to restore the deviated osmotic pressure in the blood
to its normal level.
4. The kidneys carry out osmoregulation by coordinating the rate of reabsorption of water and salts (especially
sodium and chloride ions) during the formation of urine.
5. The amount of water and salts in the blood will determine the osmotic pressure of the blood.
6. Reabsorption of water is controlled by the antidiuretic hormone (ADH) which is released by the posterior
pituitary gland.
7. Reabsorption of salts is controlled by the aldosterone hormone which is produced by the adrenal cortex gland.
The Mechanism of Osmoregulation
(A) When the blood osmotic pressure is high
1. The high osmotic pressure is detected by the osmoreceptors in the hypothalamus.
2. The posterior pituitary gland is stimulated to release the antidiuretic hormone (ADH).
3. The blood osmotic pressure is raised when water is lost excessively through sweating or after a salty meal
where a large amount of salt is consumed.
4. The adrenal gland is less stimulated and thus less aldosterone hormone is released.
5. Antidiuretic hormone increases the permeability of the walls of the distal convoluted tubule and the collecting
duct towards water.
6. Hence, more water and less salt are reabsorbed from the tubules into the blood capillaries.
7. This lowers the blood osmotic pressure to its optimum level. As a result, a small amount of concentrated urine
is produced.
( B ) When the blood osmotic pressure is low
1. The blood osmotic pressure is lowered when an excessive amount of water is consumed.
2. The low osmotic pressure in the blood is detected by the osmoreceptors in the hypothalamus.
3. The adrenal gland is stimulated to release the aldosterone hormone.
4. The pituitary gland is less stimulated and the release of ADH is greatly reduced.
5. The aldosterone hormone causes the walls of the distal convoluted tubule and the collecting duct to become
more permeable to salts and less permeable to water.
6. Hence, more salt and less water are reabsorbed from the tubules into the blood capillaries.
7. This increases the blood osmotic pressure to its optimum level.
8. As a result, a large amount of diluted urine is produced.

Consequences of Impaired Kidney Function
1. For patients with impaired kidney function, the kidney cannot remove
the excess water, mineral salt or urea. Hence, these substances remain
in the blood.
2. Kidneys that are damaged by disease or injury fail to carry out
ultrafiltration at the glomerulus, thus unable to regulate the blood
osmotic pressure, filter the blood and remove the unwanted waste
products. These problems can be overcome through haemodialysis.
3. Haemodialysis is treatment takes about six hours, and most dialysis
patients require three treatments per week.
4. During haemodialysis, blood from the artery is passed through the
machine which contains a dialyser (also called an artificial kidney).
5. The dialyser has two sections separated by a semi-permeable
membrane.
6. Blood passes on one side of the membrane and the dialysis solution
passes on the other.
7. Blood passes on one side of the membrane and the dialysis solution
passes on the other.
8. The concentration gradient between the blood and the dialysis
solution is such that the excess salts and waste molecules such as
urea can diffuse through the membrane from the blood into the
dialysis solution while blood cells and plasma proteins remain within the blood.
9. Glucose and other required substances that diffuse out of the blood may also be restored by the dialysis
solution.
10. The blood is then returned to the body.
11. Another treatment for impaired kidney functions is the transplant of a healthy kidney from a donor to the
patient.
 However, there is a risk that the recipient's body may reject the transplanted organ.
 Medicines to counteract organ rejection are used by the patients and this has greatly increased the
number of successful kidney transplants.
 In kidney transplant, a new kidney is placed inside the lower abdomen. The artery and the vein of the
new kidney are connected to the aorta and vena cava. The damaged kidneys are left in place unless
they are causing infection or high blood pressure.
Regulation of blood sugar level
1. The normal blood glucose concentration in humans is about 75 -110 mg of glucose in 100 cm3
of blood.
2. This level of glucose is regulated by the negative feedback mechanism controlled by hormones.
3. Two organs are involved:
i. Pancreas
 Small clusters of cells called islets of Langerhans consist of alpha cells ( cells) and beta cells (
cells). The  cells secrete glucagon while the  cells secrete the insulin directly into the blood.
ii. Liver
 The main target organ of insulin and glucagon is the liver. Hence, the hormones are quickly
carried in the blood from the pancreas by the hepatic portal vein to the liver where the
hormones act.

4. Insulin converts the excess glucose in the blood to glycogen which is stored as granules in the cytoplasm of the
liver cells and the muscle cells. The conversion of glucose to glycogen lowers the blood glucose concentration
to its optimum level.
5. In liver cells, the excess glucose in the blood will be converted to lipids. Meanwhile, the cells will also use up the
glucose in respiration.
6. Glucagon converts the stored glycogen in the liver (and muscles) to glucose. The glucose then diffuse out of the
liver cells into the blood. Glucagon also increases the conversion of glucose from amino acids and fatty acids in
the liver cells. This increases the blood glucose concentration to its optimum level.
Regulation of blood glucose concentration
The regulation of body temperature ( Thermoregulation )
1. The human body temperature is regulated homeostatically so that it is always maintained at a constant
temperature of about 37°C despite the changes in the environmental temperature.
2. This temperature is the optimum temperature for the reactions of enzymes in the body.
3. If the body temperature is above 40°C, enzymes will be denatured. If the body temperature is too low, the
enzyme reactions are slowed down.
4. The skin plays an important role in thermoregulation. This is because the skin can regulate the heat gain and
heat loss from the body to maintain a constant body temperature.
5. Receptors which detect the changes in temperature are called thermoreceptors.
6. In the skin, the thermoreceptors detect the changes in the environmental temperature while thermoreceptors
in the hypothalamus detect the changes in the temperature of the blood flowing near this region.

7. Thermoreceptors detect the stimulus and are stimulated. Then, nerve impulses are transmitted along the
afferent nerve to the hypothalamus.
8. The hypothalamus acts as the thermoregulatory centre (coordination centre) which transmits nerve impulses
to various effectors such as
 the sweat glands,
 hair erector muscles,
 skeletal muscles and
 endocrine glands.
These effectors produce corrective responses by negative feedback mechanism to return the body
temperature to the normal level.
9. Thermoregulatory effector response is accomplished 完成 through the changes in metabolic heat production
and physical heat loss regulation.
The action of the effectors in regulating the body temperature
By physical method ( involving skin to regulate heat loss )
Action of effectors In a warm environment In a cold environment
1. Action of sweat
glands
The sweat glands are stimulated to
produce sweat.
 Excess body heat is lost through
sweating. This gives a cooling effect
to the body.
The sweat glands are not stimulated and
thus no sweat is produced. Heat loss is
reduced.
2. Action of blood
capillaries in skin
Vasodilation process
 Vasodilation occurs. Blood capillaries
dilate and increase their diameter.
Thus, more blood flows near the body
surface.
 Excess heat in the body is lost through
conduction and radiation to the
environment
Vasoconstriction process
 Vasoconstriction occurs. Blood
capillaries constrict and decrease their
diameter. Thus, less blood flows near
the body surface.
 Most blood is diverted further from
the body surface. Hence, heat loss
through conduction and radiation is
reduced.
3. Action of hair
erector muscles
Relaxation of hair erector muscles
 Hair erector muscles relax, causing
the hair to lie flat.
 Only a thin layer of air is trapped
between the hairs. Heat loss through
conduction and radiation is increased.
Contraction of hair erector muscles
 Hair erector muscles are stimulated to
contract, causing the hairs to be
pulled and erect.
 A thick layer of air is trapped between
the hairs. The thick trapped air is a
poor conductor of heat. Thus, less
heat is lost through conduction and
radiation.

Negative feedback mechanisms in human thermoregulation

Chapter 3 Response and Coordination Notes

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Chapter 3 Response and Coordination Notes